The Legion of Superheroes was produced by Warner Brothers Animation and takes place in the 31st century. It draws on the rich history of the earlier DC comic book title Superboy and The Legion of Superheroes. Likewise, Superman is still a teenager and he is about to make the move to Metropolis. But before he leaves Smallville he gets some company from his futuristic friends the Legion. The highlight of the show was that we got to see many of the classic Legionnaires like Phantom Girl, Bouncing Boy and Brainiac 5. The series lasted for two seasons (26 episodes total) and at this point and time, Warner Brothers has only released the first season on DVD.
As the story went, the Legion intended to travel back in time to the period of when Superman was a man, but unfortunately they went back too far. The Legion had to act fast so they bring the young Clark regardless of his age, and forward him to the 31st century. Once in the future, Clark visits a museum where his Superman costume is on display. He puts on the costume and becomes young Superman. The Superman suit barely fits his younger body frame, but he is seen wearing the classic Superman costume throughout the entire series. Clark befriends the Legion and stays to serve the United Planets until he is ready to go back home.
It is easy to notice that this Superman is a younger version of Superman and the name Superboy would have been more fitting. In fact, this Superman should have been called Superboy if we are to go by the DC universe comic book line from the 50's, 60's and 70's. And yet, even in the first episode of this series Clark is called Superman rather than Superboy and he is still a teenager. So there is some argument as to why Clark is called Superman and not Superboy when traditionally the Legion has always fought alongside with Superboy. One argument is that the pending litigation regarding the Superboy character name could be the reason for calling the Boy of Steel Superman when he should have been called Superboy.
The first two episodes of season two are my own personal favorites called "The Man from the Edge of Tomorrow" Part 1 and 2. The character they meet is Superman, or, most popularly known as Superman X. Superman X is quite the mystery, cloned directly from Superman's DNA and it is probably the most intriguing storyline in this kids show. You can watch the two-part episodes below.
DC Universe Classics has released a classic Legion of Superhero's toy line with the Legion Ring (and Proty). You can read an article on it here.